The known navigation aid systems have means available for computing trajectories between waypoints defined in a flight plan entered by the pilot. The trajectories, computed at the start of a flight and possibly re-updated during the flight, are a support for the manoeuvres of the aircraft, as decided by the pilot or by an automatic piloting system. In the known state of the art, the computed trajectory is split between a lateral trajectory, typically characterized by waypoints defined by a latitude and a longitude, and a vertical profile applied to this lateral trajectory to take account of the constraints, for example of relief or of fuel consumption management.
Among the navigation aid systems, there are known flight management systems, called FMS, a functional architecture of which is schematically represented in FIG. 1. According to the ARINC702 standard, they notably handle the functions of:
Navigation LOCNAV, 170, to perform the optimal locating of the aircraft as a function of geolocation means (GPS, GALILEO, VHF radio beacons, inertial units, etc.),
Flight plan FPLN, 110, to input the geographic elements that make up the skeleton of the route to be followed (departure and arrival procedures, waypoints, etc.),
Navigation database NAVDB 130, to construct geographic routes and procedures from data included in the bases (points, beacons, interception or altitude legs, etc.),
Performance database, PERF DB 150, containing the aerodynamic and engine parameters of the aircraft,
Lateral trajectory TRAJ, 120, to construct a continuous trajectory from the points of the flight plan, observing the aeroplane performance levels and the containment constraints,
Predictions PRED, 140, to construct an optimized vertical profile on the lateral trajectory,
Guidance, GUID 200, to guide the aircraft, in the lateral and vertical planes, on its 3D trajectory, while optimizing the speed,
Digital data link DATALINK, 180, to communicate with the control centres and other aircraft.
From the flight plan FPLN defined by the pilot, a lateral trajectory is determined as a function of the geometry between the waypoints. From this lateral trajectory, a prediction function PRED defines an optimized vertical profile taking account of any altitude, speed and time constraints. For that, the FMS system has performance tables PERFDB, which define the modelling of the aerodynamics and of the engines. The prediction function PRED implements the aircraft dynamic equations. These equations are based numerically on values contained in the performance tables for computing drag, air lift, and thrust. By double integration, the speed vector and the position vector of the aeroplane are deduced therefrom.
Taking into account the meteorological conditions and their changes adds to the complexity of the computation of a flight trajectory. FIGS. 2a and 2b represent a great circle trajectory 10 between a point A and a point B. The meteorological conditions in the environment of the trajectory are represented by means of a meshing Mw, the line and the length of the arrows at each node of the meshing M illustrating the line and the intensity of the wind vector W at this node. The wind vector is defined according to the 3 dimensions; FIGS. 2a and 2b present the projection of the wind in the plane xy.
Since the wind is not constant over the journey, the great circle trajectory 10, the shortest trajectory to link A and B, does not prove the most fuel efficient and/or the fastest. An overall optimization computation of the trajectory such as, for example, dynamic programming makes it possible to construct a trajectory 11 to link the point A and the point B optimally, in terms of fuel consumption and/or in terms of time. Such a computation of an optimized trajectory as a function of the meteorological conditions requires significant computation resources and lengthy computation time. This computation can be done in a computation station on the ground, but it is relatively unsuited to a use in an embedded flight management system.
Enriching the trajectory computation of the embedded flight management systems of FMS type has been considered, by proposing means for diverting an aircraft from its trajectory on the basis of wind information. Thus, there is known, from the applicant, the patent document published under the reference FR2939505 describing an embedded solution of optimizing the lateral trajectory relying on a local modification of the flight plan. The diversion is based on the DIRTO function known to those skilled in the art, and described in the ARINC702 standard. The trajectory is modified in relation to the initial trajectory by adding a diversion point replacing a series of waypoints of the flight plan. The use of the DIRTO function necessarily restricts the complexity of the representation of the lateral trajectory to be followed. This implementation does not guarantee obtaining an optimal trajectory in terms of fuel consumption and/or in terms of time.
It is therefore still desirable to have effective navigation aid means to adapt, onboard the aircraft, a flight trajectory by making it possible to take account of a change in the meteorological conditions in order to optimize the cost of a journey. It is also advantageous to best optimize the fuel consumption and the speed by constructing a trajectory in which the aircraft is, as much as possible, pushed by the wind.
One aim of the present invention is to mitigate the above-mentioned drawbacks by proposing a navigation aid method that makes it possible to generate, from a reference trajectory, an improved trajectory that makes it possible to better use the wind, by using less computation resources than in the prior art, compatible with execution by the flight management system (FMS) embedded in the aircraft.